Optimization of Channel Structure of Alkaline Water Electrolyzer by Using an Expanded Mesh as a Bipolar Plate

Abstract

Alkaline water electrolysis (AWE) is the most mature technology for hydrogen production by water electrolysis. Alkaline water electrolyzer consists of multiple electrolysis cells, and a single cell consists of a diaphragm, electrodes, bipolar plates and end plates, etc. The existing industrial bipolar plate channel is concave-convex structure, which is manufactured by complicated and high-cost mold punching. This structure still results in uneven electrolyte flow and low current density in the electrolytic cell, further increasing in energy consumption and cost of AWE. Thereby, in this article, the electrochemical and flow model is firstly constructed, based on the existing industrial concave and convex flow channel structure of bipolar plate, to study the current density, electrolyte flow and bubble distribution in the electrolysis cell. The reliability of the model was verified by comparison with experimental data in literature. Among which, the electrochemical current density affects the bubble yield, on the other hand, the generated bubbles cover the electrode surface, affecting the active specific surface area and ohmic resistance, which in turn affects the electrochemical reaction. The result indicates that the flow velocity near the bottom of the concave ball approaches zero, while the flow velocity on the convex ball surface is significantly higher. Additionally, vortices are observed within the flow channel structure, leading to an uneven distribution of electrolyte. Next, modelling is used to optimize the bipolar plate structure of AWE by simulating the electrochemistry and fluid flow performances of four kinds of structures, namely, concave and convex, rhombus, wedge and expanded mesh, in the bipolar plate of alkaline water electrolyzer. The results show that the expanded mesh channel structure has the largest current density of 3330 A/m² and electrolyte flow velocity of 0.507 m/s in the electrolytic cell. Under the same current density, the electrolytic cell with the expanded mesh runner structure has the smallest potential and energy consumption. This work provides a useful guide for the comprehensive understanding and optimization of channel structures, and a theoretical basis for the design of large-scale electrolyzer.

Keywords

Alkaline water electrolyzer / expanded mesh channel structure / Numerical simulation

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